X-ray film identification means

ABSTRACT

In an x-ray cassette into which a flat light-emitting unit can be inserted through a slot to expose identifying markings on film, improved guiding means are provided for locating the marking unit correctly within the cassette. The guiding means include a track with an entry lip for directing the marking unit, a resilient pad supporting the track and being compressible until a stop on the track engages an inner surface of the cassette, and means in the slot which permit entry of the unit but prevent passage of light into the cassette.

United States Patent [1 1 Byler et al.

[451 Oct. 29, 1974 X-RAY FILM IDENTIFICATION MEANS [75] Inventors: William H. Byler, Landing, N.J.;

Halsey L. Rafi'man, Brooklyn, N.Y.; Frank Mast, Morristown, NJ.

I 73] Assignee: United States Radium Corporation, Morristown, NJ.

[22] Filed: Sept. 16, 1971 [2|] Appl. No.: 181,060

Related US. Application Data {63] Continuation-impart of Ser. No. l4,024, Feb. 25,

1970, Pat. NO. 3,63l,243.

[52] US. Cl. 250/476, 250/48l [5 l] Int. Cl. (301) 41/16 [58] Field of Search 250/67 [56] References Cited UNITED STATES PATENTS 3,452,196 6/!969 Gray 250/67 3,466,440 9/1969 Tone 250/67 Primary Examiner-James W. Lawrence Assistant ExaminerC. E. Church Attorney, Agent, or Firm-Pennie & Edmonds [57] ABSTRACT in an x-ray cassette into which a flat light-emitting unit can be inserted through a slot to expose identifying markings on film, improved guiding means are pro vided for locating the marking unit correctly within the cassette. The guiding means include a track with an entry lip for directing the marking unit, a resilient pad supporting the track and being compressible until a stop on the track engages an inner surface of the cassette, and means in the slot which permit entry of the unit but prevent passage of light into the cassette.

7 Claims, 14 Drawing Figures PMENTEUDU 29 Ian L. RAFFMAN ATTORNEYS PAIENIEllocras m4 38453 1 4 m u or 4 X 60 FIG. 12

I VENTORS WIL IAM H. BYLER HAL EY L.RAFFMAN FRANK MASI BY PM Jun, ML WM ATTORNEYS 1 X-RAY FILM IDENTIFICATION MEANS RELATED CASE This application is a continuation-in-part of our copending application Ser. No. l4,024 filed Feb. 25, I970 for Method And Means For Film Identification and now US. Pat. No. 3,631,243.

BACKGROUND OF THE INVENTION In our co-pending application referred to above, a method and means are disclosed for identifying film exposures in an x-ray cassette or other camera-like housing. The system employs a phosphorescent marking unit activated by incident radiation and inserted through a light-sealed aperture so that its diminishing afterglow casts the silhouette of certain indicia on the film. A particular form of slot in the cassette, the asso ciated light-seal assembly and interior means for urging the inserted marking unit against the film are all shown in the aforementioned co-pending case.

Other forms of guiding means have also been known in the prior art for directing a light-emitting marking unit into proper position with respect to the film. For example F. F. Tone et al. US. Pat. No. 3,488,753 describes elements generally of that sort. However, neither that patent nor any other reference prior to our aforementioned co-pending application disclosed or suggested guiding means designed to direct a thin phosphorescent light-emitting unit into place to mark film in an xray cassette.

The principal object of this invention is to provide simple and reliable guiding means for locating a flat light-emitting unit inside an x-ray cassette to expose identifying markings on the film. This is to be achieved by a combination of elements which function together in an improved manner in comparison to the guiding means shown in our aforementioned application and in the prior art. In particular, it is an object of this invention to control to a large extent the force urging the marking unit against the film within the cassette and also the frictional force resisting movement of the marking unit into and out of operating position.

SUMMARY OF THE INVENTION Broadly stated, the invention is for use with an x-ray cassette including a shallow body adapted to enclose film and a slot into which a flat light-emitting unit can be inserted to expose identifying markings on the film. Improved guiding means are provided for locating the unit inside the cassette with respect to the film. The guiding means comprise a track within the cassette against which the unit is slideable as it is inserted through the slot. The track includes an entry lip at one end for directing the unit between the track and the film. It also includes stop means. A pad supports the track within the cassette for urging the track resiliently toward the film. The pad is compressible until the stop means engages an inner surface of the cassette. Finally, means are located in the slot to permit entry of the unit but to prevent passage of light into the cassette.

In more specific forms of the improved guiding means, the track includes a central longitudinal indentation and the pad is formed with a central longitudinal cut-out portion. A lid may be hinged to one edge portion of the body and in that case the slot may be defined between the edge portion of the body and part of that edge of the lid which is hinged to the body.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view, partly broken away, of one embodiment of an x-ray cassette adapted to the invention;

FIG. 2 is a perspective of the same cassette fully closed and illustrating the associated insertion unit;

FIG. 3 is an enlarged fragmentary section partly broken away of the cassette taken along the line 3-3 of FIG. 2;

FIG. 4 is a graph showing the relationship of light output from the insertion unit to film sensitivity against time;

FIG. 5 is a composite perspective showing the label and carrier sheet of one form of the insertion unit;

FIG. 6 is an enlarged fragmentary section of the insertion unit of FIG. 5;

FIG. 7 is a composite perspective showing the label and carrier sheet of another form of the insertion unit;

FIG. 8 is an enlarged fragmentary section of the insertion unit of FIG. 7;

FIG. 9 is a perspective view of another embodiment of a closed cassette adapted to the invention and again illustrating the associated insertion unit;

FIG. 10 is a fragmentary enlarged plan view of the cassette of FIG. 9 in the open position showing the improved guiding means;

FIG. 11 is a section taken along the line 11-11 of FIG. 10;

FIG. I2 is a section similar to that of FIG. II but with the cassette closed and illustrating the associated insertion unit;

FIG. 13 is a perspective view of the foam pad of the improved guiding means; and

FIG. I4 is a perspective view of the track of the improved guiding means.

Referring first to FIGS. 1 to 3, a cassette 10 is shown which includes a lid 11, a channel frame 12, and a front panel 13. The lid, which is in the open position in FIG. I and closed in FIGS. 2 and 3, is hinged to the frame I2 and the front panel 13 is fixed in the frame 12, all in the conventional manner. Latches 14 on the frame I2 serve to releaseably secure the lid 11 in closed position.

The customary interior elements of the cassette 10 include at least the following: Inside the lid 11 is a felt pressure pad I5 (lead foil may be disposed between them). On the interior side of the pad 15 is a rear intensifying screen 16 of fluorescent material, the function of which is to convert x-ray energy to visible light. Next is photographic x-ray film l7. Immediately on the other side of the film I7 is a front intensifying screen 18 similar in structure and function to the rear screen 16. Between the front intensifying screen I8 and the front panel 13 is another pressure pad I9.

In a typical cassette, the two intensifying screens and the film are removable while the pressure pads are adhered in place. When the lid I1 is closed the interior elements of the cassette are held tightly together due to the resiliency of the pads 15 and 19. The film I7 is thereby completely enclosed within a tight opaque housing.

In use the subject to be diagnosed is placed before the front panel 13 and x-rays are directed through the subject and into the cassette 10. When the x-rays strike the intensifying screens 16 and I8 they cause them to glow and that visible light in turn exposes the film 17. Those portions of the subject which are less permeable to x-rays cast what is in effect a shadow on the intensifying screens and the image of it is thereby recorded on the film.

The object of the present invention is to record on the film not only the image of the subject being diagnosed but also the image of the patient's name or other identifying data useful in interpreting the x-ray photograph.

For this purpose a light-sealed aperture is provided in the cassette to receive an insertion unit 2]. The insertion unit 21 is generally illustrated in FIGS. 2 and 3 (specific forms are described in detail hereinafter). It includes a plastic carrier sheet 22 which is flexible but sufficiently rigid to be pushed into the cassette without buckling. The carrier sheet includes an insert portion 23 and a wider tab portion 24 so that its overall configuration is T-shaped. A translucent label 25 is adhered to the insert portion 23 of the unit and indicia 26 setting forth the desired information are typed on the face of the label. Somewhere behind the typed indicia 26 the insertion unit includes phosphorescent material which is activated by incident radiation to emit light, and that light silhouettes the typed indicia 26.

One form of guiding means is shown in FIGS. 1 to 3 for permitting the unit 2l to be inserted into the cats sette and withdrawn during operation. Such means include a slot 28 formed in the lid 11 and angling inwardly as shown in FIG. 3. The pressure pad inside the lid I1 is cut away as shown in FIGS. l and 3, and so also is the intensifying screen 16 on the interior surface of the pad 15. A resilient light-seal assembly 29 attached by rivets 30 occupies the cut-out area of the pad 15. It is composed of two felt-like flaps 3i and 32 separated by a flexible tongue 33, all biased together by a leaf spring 34 so that the entire assembly presses resiliently toward an opposed bevelled surface 35 on the pad 15 to seal the interior of the cassette against entry of ambient light. These parts of the apparatus provide guiding means in the cassette for properly positioning the insertion unit 21.

To the other side of the front intensifying screen 18 from the light-seal assembly is a rectangular lead blocker 36 of approximately the same width as the cutout portion of the screen 16. As shown the blocker 36 is seated in the inner face of the front panel 13 and oc cupies a cut-out area in the pressure pad 19. As an alternative, the screen 18 may be formed with a cut-out area coincident with the area shown to be covered by the blocker 36. or an opaque layer may be deposited on the screen 18 in that area on the side thereof facing the film [7. If the x-ray intensity is relatively high, the blocker may be used together with a cut out in the screen [8. These represent several methods which may be used for preventing x-ray activated illumination from exposing the film 17 in the region thereof coincident with the cut-out area of the screen 16 to the right of the light-seal assembly 29 as seen in FIG. 3.

By this construction the insertion unit 21 can be gripped manually at its tab portion 24 and the insert portion 23 thereof can be directed through the slot 28 in the closed lid 11 of the cassette [0. The end of the insert portion 23 is thus forced past the fiap 31 and bends around the beveled surface 35 on the pad 15 so that it can slide fully into the cut-out area of the screen 16 along the rearward face of the film. The insertion unit is oriented during this procedure so that its label 25 will face forward in contact with the film 17 in the inserted position.

In the inserted position, the phosphorescent material incorporated in the insertion unit (in a manner de' scribed hereinafter) casts the silhouette of the indicia 26 on the surface of film 17 in the rectangular area of the film 17 which is protected by the blocker 36 or other means and hence is otherwise unexposed. The afterglow from the insertion unit thereby exposes the image of the indicia on the film.

The phosphorescent material is preferably a phosphor such as copper-activated zinc sulfide. lts light output should be sufficiently limited so that it does not expose the film during the brief period the unit 21 is moving into position during insertion. The output of light should be great enough, however, so that during the hold period the film becomes legibly exposed with the image of the indicia. Many phosphors can be matched with most x-ray films to achieve these objects. There is another characteristic of phosphors which can be selected to produce one of the most significant advantages of the invention, and that is the property of afterglow decay rate. After excitation by exposure to incident light, a phosphorescent material glows but at a diminishing level. After a short time it emits virtually no light at all.

FIG. 4 is a graph showing the cumulative light output of a representative phosphor plotted against time. It will be seen that during the brief period required for inserting the unit the light output is quite low (e.g. 0.4 seconds) and hence does not cause smearing of the film while the indicia are in motion. It is also apparent that the hold time (e.g. 4 or 5 seconds) for achieving proper exposure is relatively short. Finally the FIG. 4 graph shows the diminishing afterglow from the phosphor does not add significantly to the cumulative light output after the recommended hold period is complete, and hence no matter how long the unit is left in place it will not reach the over-exposure level of the film. In practice this means that even though an insertion unit may be left inside a cassette too long by mistake, the film therewithin will still be legibly printed with the identifying data. Timely withdrawal after the specified hold period is not critical. and the chance of error in the identification process is greatly reduced.

A phosphor which exhibits a so called power law or hyperbolic brightness decay rate is preferred for this purpose. In addition to copper-activated zinc sulfide, silver-activated zinc sulfide or zinc cadmium sulfide and copper-activated zinc cadmium sulfide also can be employed. By varying such properties as emission color. these phosphors may be adapted for use with film of different speed or sinsitivity.

In the form of insertion unit shown in FIGS. 5 and 6, the carrier sheet 22A is of a plastic such a polytetrafiuorethylene. While it is flexible, it has sufficient column strength to penetrate the light-sealed aperture of the cassette without buckling. A label 25A is employed which is of paper, plastic or other suitable material. Covering one surface of the label 25A is a layer 39 of uniformly dispersed fine crystals of a phosphor such as copper-activated zinc sulfide. Typed. printed or otherwise marked on the exposed face of the layer 39 is all the identifying data desired. This may include not only the patient's name and so on but also the time of the xray, an important item of information in many x-ray techniques where progressive change is to be observed. The label could be automatically stamped with the time by means of an appropriate clock-printer into which the radiologist may insert the unit.

On the surface of the label 25A opposite the phos phor layer 39 is a coating 40 of pressure-sensitive adhe-- sive. The label 25A may advantageously be torn along perforation lines from a larger sheet containing many labels, and the coatings of pressure-sensitive adhesive and phosphor may cover the entire sheet. Prior to the use of the label 25A, its adhesive coating 40 is pro tected by a strip sheet 41 which can be discarded after it is removed.

In operation, the label 25A is typed or stamped directly on its phosphor layer 39 as desired, its strip sheet 4] is removed to expose the pressure sensitive adhesive 40 and it is then applied to the insert portion of the carrier sheet 22A. Just before or after the patients x-ray is taken, the phosphor on the label is made to flow by exposure to incident radiation, which may be simply the ambient light in the room. The carrier sheet 22A is then thrust into the cassette through the aperture 28 and held there for a count of four seconds. During this time the afterflow from the phosphor casts the silhouette of the indicia on the film 17, with little penumbra effect since the phosphor layer and indicia are in direct contact with one another and with the film. After this hold period the operator pulls out the insertion unit and identification is complete.

The unit can be used again for any number of additional x-rays the patient may have taken. (As the x-rays are taken, the area of the film reserved for the identification is isolated by the blocker 36 from any light emitted by the intensifying screens 16 and I8.) Before each insertion, proper charging of the phosphor by exposure to incident light should be insured. After the film in all the cassettes is marked, the label 25A is removed from the carrier sheet 22A and discarded.

In the form of insertion unit illustrated in FIGS. 7 and 8, a carrier sheet 228 is provided with a dry coating 45 of phosphor. A label 255 used therewith has only pressure-sensitive adhesive 36 disposed on the side opposite the indicia. To protect the adhesive prior to use a disposable strip sheet 47 is provided. This embodiment differs from that of FIGS. 5 and 6 in that the phosphor is on the carrier sheet rather than the label before the two are brought together. In the assembly there is less close spacing between the phosphor and the indicia than in the prior embodiment because here the adhesive and the label stock lie between. Hence, there is a theoretically greater chance of some slight fogging due to a larger penumbra.

Many variations can be made in the procedures and devices described above without departing from the essential concept of the invention. Rather than use a label. indicia could be placed directly on a phosphor coated element similar to the carrier sheet 228. It is conceivable to mix the phosphor with the adhesive or apply it as a coating on the carrier sheet, or the phosphor could be uniformly dispersed in the body of the carrier sheet or of the label, or the carrier sheet could be made translucent and the phosphor disposed on the side thereof opposite the label. Adhesive can be located on the carrier sheet rather than the label and it need not be pressure sensitive. It is also possible that the insertion unit be a shape other than flat. in order to be used with film-containing housings other than x-ray cassettes.

An improved form of guiding means is provided by the invention as illustrated in FIGS. 9 to 14. Referring first to FIG. 9, a cassette is shown in closed position. It includes a lid 51 and a channel frame 52 to which the lid isjoined by hinges 53 and 53A. Latches 54 and 54A serve to secure the lid 5] releasably in closed position.

As shown in FIGS. 11 and 12, the cassette includes a front panel 55. Inside the lid is a felt pressure pad and a rear intensifying screen similar to the pad 15 and screen I6 of FIGS. 1 and 3. Adjacent to the rear screen is photographic x-ray film 56 and on the other side of the film is a front intensifying screen 57. Between the front intensifying screen 57 and the front panel is another pressure pad 58.

The procedure for insertion and withdrawal of a marking unit with the cassette of FIGS. 9 to 14 is similar to that described in relation to the embodiments of FIGS. I to 8. A marking unit 59 is therefor shown in FIGS. 9 and 12 in position to be inserted into the cassette.

In the preferred form ofthe improved guiding means, the cassette includes a slot 60 defined between an edge of the lid 51 adjacent the hinge 53 and the adjoining edge portion of the channel frame 52. The slot 60 is made simply by removing part of an inwardly directed flange 61 formed around the perimeter of the lid 51.

As shown particularly in FIGS. 11 and 12, the channel frame 52 includes an inwardly projecting flange 62 which underlies the lid flange 61 on the lid 51 when the lid is in closed position. in the region of the slot 60, this flange 62 on the channel frame provides a support for a light-seal formed ofa brush 63 with polyethylene bristles. When the lid 51 is closed, the underside of the lid adjacent the slot 60 engages the outer end of the bristles 63 as shown in FIG. 12 and prevents passage of light into the cassette. At the same time the bristles 63 can be displaced to permit insertion of the unit 59. The bristles may be mounted on a plastic backing 64 which in turn is secured by adhesive to the flange 62 of the channel frame 52.

After the unit 59 has passed the light-seal during its insertion, it next encounters a metal track 65 which is designed to direct the unit into proper position with respect to the x-ray film 56. The track 65 is shown assembled with the other parts in FIGS. 10 to 12 and individually in FIG. 14. It includes a central portion divided by a longitudinal indentation 67 formed so that the unit 59 slides only against that portion of the track to each side of the indentation 67. As a consequence the frictional resistance of the track to movement of the unit 59 is reduced. Another function of the indentation 67 is that it serves to strengthen the track and make it more rigid. This is of importance because the track should be as flat as possible to maintain an even bearing pressure on the insertion unit 59.

At the end of the track 65 nearest the slot 60, an entry lip 68 is formed for guiding the unit 59 between the track and the film 56. The opposite end of the track 65 is formed with a turned in edge which serves as a stop projection 69.

As shown in FIG. 12, a foam pad 70 supports the track within the cassette [in FIG. 13 the pad is shown in full perspective). The function ofthe pad is to urge the track 65 resiliently toward the film 56. A central cut-out portion 71 is formed in the pad 70 to control the amount of resilient spring force it exerts on the track, ie the larger the area of the cut-out portion 71, the less spring force exerted by the pad 70 on the track 65, and vice versa. The thickness of the pad 70 is such that the stop projection 69 on the track 65 is spaced from the inside surface of the lid SI as shown in FIG.

12 when the lid SI is closed and the track and film are in face-to-face engagement. When the insertion unit 59 is directed between the track 65 and the film 56, the track is moved upwardly as shown in FIG. 12 to compress the pad 70. Such compression of the pad cannot go beyond the point where the stop projection 69 contacts the underside of the lid SI. The preferred material for the pad 70 is relatively soft silicone foam.

As in the embodiment of FIGS. I to 3, the felt pad 58 is cut away and a lead blocker 72 is positioned in the region where the unit 59 is to be inserted. The function of the blocker is to prevent x-rays from energizing the intensifying screen 57 in the area where the identifying markings are to be placed in the film. As shown in FIG. 10. a cutout 73 is formed in the corner of the rear intensifying screen so that the track 65 may directly contact the film 56 when the lid Sl is closed.

In operation. the film 56 is loaded within the cassette in the usual manner and the light-emitting phosphorescent insertion unit 59 is prepared with its identifying data as described in relation to FIGS. I to 8. When the lid SI is closed. the track 65 is thereby brought down resiliently against the corner area of the film 56 where the identifying markings are to be placed. The unit 59 is then inserted through the slot 60 and past the bristles of the light-seal assembly 63. The forward end of the unit 59 then reaches the entry lip 69 at the end of the track 65, and the lip 68 guides the unit 59 between the track and the film. Further movement of the unit 59 causes it the slide over the surface of the track (except in the area ofthe indentation 67) and to force the track 65 against the resilient pad 70. The pad 70 in turn compresses but not beyond the point determined by the stop projection 69. Under the force of the pad 70 acting through the track 65, the insertion unit is held fiat against the film 56. In this manner. an image of the indicia on the unit is exposed on the film with a minimum of blurring.

We claim:

I. In an x-ray cassette including a shallow body adapted to enclose film and a slot into which a flat flexible light-emitting unit can be inserted to expose identifying markings on the film; improved guiding means for locating the unit inside the cassette with respect to the film comprising a. a rigid track within the cassette against which the unit is slidcable as it is inserted through the slot,

i. said track facing the enclosed film and lying in a plane parallel thereto. and

ii. said track including an entry lip at one end for directing the unit between the track and the film b. a resilient pad supporting the track within the eassette for resiliently urging the track against the unit to hold the latter flat against the enclosed film. and

c. means located in the slot to permit entry ofthe unit but to prevent passage of light into the cassette 2. The combination according to claim 1 wherein the track includes a central longitudinal indentation.

3. The combination according to claim 1 wherein the pad is formed with a central longitudinal cut-out portion.

4. The combination according to claim I wherein the cassette includes a lid hinged to one edge portion of the body. the slot being defined by the edge portion of the body and a cutout in the edge of the lid.

5. In an it-ray cassette including a shallow body adapted to enclose film and a slot into which a flat flexible light-emitting unit can be inserted to expose identifying markings on the film; improved guiding means for locating the unit inside the cassette with respect to the film comprising:

a. a rigid track within the cassette against which the unit is slideable as it is inserted through the slot,

i. said track facing the enclosed film and lying in a plane parallel thereto,

ii. said track including an entry lip at one end for directing the unit between the track and the film,

iii. a central longitudinal indentation, and iv. a stop projection at the end opposite the entry lip;

b. a resilient pad supporting the track within the eassette for resiliently urging the track against the unit to hold the latter flat against the enclosed film independently of any pressure means for holding the film in place in the cassette,

i. said pad being compressible until the stop projection engages an inner surface of the cassette,

ii. said pad being formed with a central cutout portion; and c. a brush located in the slot to permit entry of the unit but to prevent passage of light into the eassette. 6. In an x-ray cassette including a shallow body adapted to enclose film, a lid hinged to one edge portion of the body and a slot in the cassette into which a flat flexible phosphorescent light-emitting unit can be inserted to expose identifying markings on the film; improved guiding means for locating the unit inside the cassette with respect to the film comprising a. a metal track within the cassette against which the unit slides as it is inserted through the slot, said track including i. an entry lip at one end which directs the unit between the track and the film,

ii. a central longitudinal indentation, and

iii. a stop projection at the end opposite the entry b. a foam pad supporting the tract within the cassette and urging it resiliently toward the film,

i. said pad being compressible until the stop projection engages an inner surface of the cassette,

ii. said pad being formed with a central cut-out portion; and

c. a brush located in the slot to permit entry of the unit while preventing passage of light into the cassette;

d. said slot being defined between an edge portion of the body and part of that edge of the lid which is hinged to the body.

7. The combination according to claim 6 wherein the pad is of silocone foam and the brush is formed with polyethylene bristles.

I k k K UNITED, STATES PATENT OFFICE CERTIFICATE OF CORRECTION natecpct'ober 29 1974 Pacent No. 3 I 5 314 bflgWilliam H. Byler, Halsey L. Raffman and Frank Masi It is certified that: error appears in the above-identified patent and that. said Letters Patent are hereby corrected as shown below:

Title Page, under heading "Inventors, "Frank Mast, should read .--Frank Masi--.

Column 5, line 44, "adhesive 36 should read adhesive 46-.

Column 7; line 38, "causes it the" should read causes it to Signed and sealed this 7th day of' January 1975.

(SEAL)- Arrest:

c. MARSHALL DANN Commissioner of Patents MeCOY M. GIBSON JR; Attesting Qfficer 

1. In an x-ray cassette including a shallow body adapted to enclose film and a slot into which a flat flexible light-emitting unit can be inserted to expose identifying markings on the film; improved guiding means for locating the unit inside the cassette with respect to the film comprising a. a rigid track within the cassette against which the unit is slideable as it is inserted through the slot, i. said track facing the enclosed film and lying in a plane parallel thereto, and ii. said track including an entry lip at one end for directing the unit between the track and the film b. a resilient pad supporting the track within the cassette for resiliently urging the track against the unit to hold the latter flat against the enclosed film, and c. means located in the slot to permit entry of the unit but to prevent passage of light into the cassette.
 2. The combination according to claim 1 wherein the track includes a central longitudinal indentation.
 3. The combination according to claim 1 wherein the pad is formed with a central longitudinal cut-out portion.
 4. The combination according to claim 1 wherein the cassette includes a lid hinged to one edge portion of the body, the slot being defined by the edge portion of the body and a cutout in the edge of the lid.
 5. In an x-ray cassette including a shallow body adapted to enclose film and a slot into which a flat flexible light-emitting unit can be inserted to expose identifying markings on the film; improved guiding means for locating the unit inside the cassette with respect to the film comprising: a. a rigid track within the cassette against which the unit is slideable as it is inserted through the slot, i. said track facing the enclosed film and lying in a plane parallel thereto, ii. said track including an entry lip at one end for directing the unit between the track and the film, iii. a central longitudinal indentation, and iv. a stop projection at the end opposite the entry lip; b. a resilient pad supporting the track within the cassette for resiliently urging the track against the unit to hold the latter flat against the enclosed film independently of any pressure means for holding the film in place in the cassette, i. said pad being compressible until the stop projection engages an inner surface of the cassette, ii. said pad being formed with a central cutout portion; and c. a brush located in the slot to permit entry of the unit but to prevent passage of light into the cassette.
 6. In an x-ray cassette including a shallow body adapted to enclose film, a lid hinged to one edge portion of the body and a slot in the cassette into which a flat flexible phosphorescent light-emitting unit can be inserted to expose identifying markings on the film; improved guiding means for locating the unit inside the cassette with respect to the film comprising a. a metal track within the cassette against which the unit slides as it is inserted through the slot, said track including i. an entry lip at one end which directs the unit between the track and the film, ii. a central longitudinal indentation, and iii. a stop projection at the end opposite the entry lip; b. a foam pad supporting the tract within the cassette and urging it resiliently toward the film, i. said pad being compressible until the stop projection engages an inner surface of the cassette, ii. said pad being formed with a central cut-out portion; and c. a brush located in the slot to permit entry of the unit while preventing passage of light into the cassette; d. said slot being defined between an edge portion of the body and part of that edge of the lid which is hinged to the body.
 7. The combination according to claim 6 wherein the pad is of silocone foam and the brush is formed with polyethylene bristles. 